مجله مواد و فناوری های پیشرفته
سال نهم شماره 3 (پاییز 1399)

Abstract     Nowadays, magnesium alloys such as a new generation of biodegradable materials have been noticed by researchers. In this study, to the sanitation of biodegradability and biocompatibility of magnesium alloys, TiO2/MgO dual layer coating was formed by magnetron sputtering on AZ91 and the microstructure, corrosion behavior and biocompatibility properties of coating were investigated. The coating microstructure was studied via field emission scanning electron microscopy (FESEM) X-ray diffraction (XRD). The corrosion resistance of the substrate and coated sample was evaluated by electrochemical polarization test in simulated body solution (SBF). To evaluate biocompatibility MTT and cell viability tests were used. The results showed that the corrosion potential after the surface coating with TiO2/ MgO was more positive, changing from 1.532 V for the uncoated sample to 1.436 V for the coated sample.. The coating was observed in quasi-spherical morphology with MgTi2O5 and MgTiO3 phases in interface of coating and substrate and two layers of coating too according to XRD analysis results. The results of the biocompatibility tests also showed that the viability of the osteoblastic cells on the coated sample increased compared to substrate.

Al/Cu bimetals have many applications in power lines. During operation and due to the crossing electrical current, bimetals are heated and the temperature increases, resulting in microstructural changes and properties alternation in the interface areas. The aim of this article is to study aging treatment of friction welded Cu/Al bimetallic joint, in the presence of electrical current. Aging of bimetals was carried out under electric currents of 250 A and 500 A, which caused the components to warm up to initial temperatures of 150 °C and 250 °C, respectively. The results show that electrical current increase from 250 A to 500 A leads to increase intermetallic grows rate and increase electrical resistance. Also, the possible stable phases at the interface are CuAl2, CuAl, Cu4Al3, and Cu3Al2.

The aim of this work is the characterization of the Co3O4 fibres, prepared by the electrospinning method. The investigation of the structural, morphological,optical, and magnetic properties of electrospun fibres at two different calcination temperatures was conducted by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Diffuse Reflectance Spectra (DRS), and Vibrating Sample Magnetometer (VSM). XRD indicates the cubic phase of the calcined Co3O4 fibres. The microstructural parameters such as crystallite size and its distribution are determined from the X-ray diffraction pattern analysis using the whole powder pattern modeling (WPPM) approach. The results obtained from the X-ray diffraction pattern analysis and crystallite size distribution shows an increase in the crystallite size with calcination temperature. The SEM images show the formation of randomly oriented fibres with diameters in the range of 200-250 nm after calcination. The DRS results show a decrease in the band gap energy with increasing calcination temperature. The magnetic analysis performed by VSM, confirms a paramagnetic phase of fibres at elevated calcination temperatur.

The purpose of this work is to make lithium-air battery with a high performance, simple design, and inexpensive. In this design, a carbon/CuFe2O4 based nanocatalyst with a particle size of ≈ 30 nm was used to modify the battery cathode. The ionic liquid of 1-hexyl-3-methylimidazolium chloride [Hmim][Cl] was used as an electrolyte with high conductivity and thermal stability to increase the safety, lifetime, and discharge capacity of the battery. Physiochemical properties of the nanocatalyst were determined by Fourier Transform Infrared Spectroscopy (FTIR), Thermal Gravimetric Analysis (TGA), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). The battery discharge capacity at a current density of 0.1 mA/cm for a battery without and with nanocatalyst was obtained 528 mAh/g and 677 mAh/g, as respectively. The charge-discharge cycles of battery containing nanocatalyst were significantly increased (up to 1000 cycles) compared to the sole battery. Low vapor pressure (boiling point > 350 °C) and high thermal stability (stability against decomposition) of the electrolyte increase battery lifetime. One of the advantages of the designed battery is low overpotential amount.

In this research, the transient liquid phase bonding process on Nimonic alloy 75 was investigated using an AWS BNi-2 interlayer with a 32 μm thickness. The transient liquid phase bonding process was performed at 1050 °C, 1100 °C, and 1150 °C for 60 min. X- ray diffraction (XRD) technique was employed to identify the Boride phases in the joint area. For the Nimonic 75 alloy, the experimental results showed that the temperature and time have an evident effect on the phase constituents of the Boride phases, i.e., CrB and Ni2B. Also, the shear strength of TLP joints was measured. The results indicated that the joint microstructure consisted of three zones, including isothermal solidification zone (ISZ), thermal solidification zone, and diffusion affected zone. The diffusion affected zone of the Nimonic 75 alloy was vanished and the homogenization process occurred by increasing the bonding time. The results of shear strength showed that the bonding strength was increased from 63 MPa to 152 MPa with increasing the bonding temperature from 1050 to 1150 °C, respectively. Analysis of fracture surfaces showed that the fracture mode changed from brittle, semi-brittle and finally ductile mode by increase in bonding temperature which is due to the decrease in volume fraction of brittle intermetallic phases and eutectic structureany sort of image, illustration, figure, or table.

In this research, a fast, environmentally friendly, and low-cost method has been used for the synthesis of large-scale production of graphene oxide. In this process, graphene oxide was synthesized via single-step reforming of sugarcane bagasse agricultural waste by oxidation under muffled atmosphere conditions at 350 ºC and for 15 minutes. The results of Fourier transform infrared spectroscopy and X-ray diffraction analyses confirm the formation of graphene oxide. The results of scanning electron microscopy and atomic force microscopy studies show that the graphene oxide sheets are with few wrinkles, the number of layers is 5-6 layers, the average size of the plate thickness is 5 nm, and the average lateral dimensions of the plates is 500 nm. The synthesized graphene oxide was evaluated by the toxicity test at concentrations of 200, 400, and 600 μg/ml on Gram-positive bacteria, “Streptococcus iniae”, and Gram-negative bacteria, “Escherichia coli” and “Pseudomonas aeruginosa”. The results show that graphene oxide at concentrations of 400 and 600 μg / ml has a toxic and an antibacterial agent for bacteria and it has reduced the growth rate of bacteria. In addition, graphene oxide nanosheets are more toxic to gram-positive bacteria than gram-negative bacteria. The results of differential thermal analysis on sugarcane bagasse show that the formation of graphene oxide in air is at a temperature of 350 °C but it is in argon atmosphere is higher. In addition, the results of the thermal analysis performed on the synthesized graphene oxide in the air atmosphere indicate that its instability begins at 60 °C.

The Biodegradable polymers with non-toxic and biocompatible nature have applications in tissue engineering and drug delivery. The use of natural polymer microbeads independently or in combination with other materials is gaining ground in various applications including injectable biomaterials. In this research, the interaction of gelatin and sodium alginate biopolymers was investigated in the manufacture of microsphere. The interaction between these two polymers was influenced by their pH, charge, and concentration. The electrostatic reaction between positively charged proteins and anionic polysaccharides led to the formation of soluble and insoluble phases. Therefore, the effect of pH and colloidal ratio was examined on the Coacervation. First, gelatin molecular weight was narrowed by Desolvation method, and GPC confirmed the elimination of low molecular weight gelatin. The supernatants of colloidal mixtures were analyzed by UV-Vis test, and the results revealed that optimum coacervation occurred at a gelatin/sodium alginate ratio of four and a pH value of 3.65. During this process, microsphere formed with smooth surfaces in a size range of 10-25 µm. An increase in the amount of genipin raised the aggregation tendency in independent microbeads. A slight change of gelatin in Circular Dichroism (CD) reflected the interaction with sodium alginate, which was confirmed by the amide functional group in the Fourier-transform infrared (FTIR) spectroscopy. Results of Thermogram of Differential Scanning Calorimetry (DSC) indicated an increase in the degradation temperature of microspheres containing higher amounts of genipin.